The present invention relates to a new method of forming a concrete column capital within the traditional panelized formwork currently used to form reinforced concrete flat slabs.
The present invention, more particularly, relates to a method of forming a concrete column capital, wherein the formwork containing and shaping the wet concrete, comprises one or more flat flexible sheets, e.g., a woven, coated or uncoated, high density polyethylene, or polypropylene fabric.
The floors of reinforced concrete buildings are sometimes formed without beams that project below the undersurface of the slab. This type of reinforced concrete slab is sometimes referred to as a "flat plate slab", because the underside of the slab is uninterrupted by supporting beams. These slabs have the advantage of being faster and easier to form, and their flat undersurfaces do not restrict, or complicate, the later installation of partition walls, ductwork, plumbing, etc., within the completed building.
Because flat plate slabs rest directly on top of the columns which support them, without the added depth of any supporting beams, they are particularly vulnerable to punching shear stresses at the column-slab junction. Sometimes a flat slab cannot provide sufficient resistance to the shear forces imposed on it by a supporting column. Under these conditions a column capital is formed between the supporting column and the flat slab it supports. This column capital provides a deeper section to the area of the flat slab near the supporting column, thus providing the added strength necessary to resist the concentrated sheer stresses that develop around a supporting column.
There are several different conventional methods of forming a concrete column capital. However, these conventional methods usually use some kind of rigid formwork material, e.g., plywood or metal panels, fiberglass reinforced moulds, etc.
Often, a single building may have several different sizes of columns, and the distance between support columns may vary considerably. Under these conditions, several different column capital forms may have to be constructed for a single building. These column capital formworks are often constructed so that they can be disassembled and removed for possible use at a different location in the building, or a different job site. The construction, removal, and re-assembly of rigid column capital forms is often not easily accomplished. These tasks involve the cutting and assembling of several different rigid pieces. In addition, conventional column capital formwork often requires a more complex shoring framework to be built below the flat slab formwork panels than would otherwise be required.
The use of a flexible tension membrane formwork to form a concrete column capital would substantially simplify many of these difficulties. Column capital formworks could be constructed out of fewer pieces, using a flexible fabric; the removal and re-assembly of capital formworks would likewise be simplified. The material costs of a fabric formwork would be many times less than even the least expensive rigid formwork material. The geometry of a column capital formed with a flexible tension membrane would be more efficient than those typically formed with plywood panels, and hence require less concrete. A flexible tension membrane formwork would obviate the requirement for the more complex shoring framework that is usually built below the flat slab formwork panels in conventional practice.